Web Browser

In Turkish: Web Tarayıcısı

Updated September 30, 20262 min read

In short

A web browser is an application that fetches web pages from servers and turns their HTML, CSS, and JavaScript into the interactive pages you see on screen.

What is a web browser?

A web browser is the program you use to visit websites. When you type a URL or click a link, the browser looks up the server's address using DNS, requests the page over HTTP or HTTPS, and displays the response. Along the way it also manages cookies, local storage, security certificates, tabs, and your history.

Inside every browser is a rendering engine that turns code into pixels. It parses HTML into the DOM, a tree of the elements on the page, applies CSS to work out how each element should look, calculates the layout, and paints the result on screen. A separate JavaScript engine runs the page's scripts, which can change the DOM in response to clicks and typing, and today almost all browsers are built on one of three engines: Blink, WebKit, or Gecko.

A browser is like a theater crew performing a script: the server sends the script, written in HTML, CSS, and JavaScript, and the browser stages it for you. Browsers also enforce security rules, such as running each site in a sandbox and applying the same-origin policy, which stops one website from reading data that belongs to another.

People often confuse the browser with a search engine or with the web itself. The browser is the application on your device, a search engine is a website you open in the browser to find other pages, and the web is the network of pages and servers the browser connects to. For developers, small differences between browsers still matter, which is why sites are tested in several browsers and debugged with the built-in developer tools.

Key takeaways

A browser requests web pages from servers and displays them.
Its rendering engine turns HTML and CSS into the DOM, a layout, and pixels.
A JavaScript engine runs page scripts that make pages interactive.
Browsers enforce security rules such as sandboxing and the same-origin policy.
A browser is not a search engine; a search engine is a website opened in a browser.

Example

Using built-in browser APIs from JavaScriptjavascript

// A few of the APIs a browser gives to scripts running on a page
console.log(window.location.href); // the current page's URL
console.log(navigator.language);   // the user's preferred language, e.g. "en-US"

// Change the DOM: the browser re-renders the page automatically
const heading = document.querySelector("h1");
heading.textContent = "Hello from the browser";

// Make a network request with the built-in Fetch API
const response = await fetch("/api/status");
console.log(response.status);

Readers ask

What is the difference between a browser and a search engine?

A browser is the application on your device that opens and displays web pages. A search engine is a website or service, used through a browser, that helps you find pages by keyword.

What is a browser engine?

A browser engine, or rendering engine, is the core component that parses HTML and CSS, lays out the page, and draws it on screen. Most modern browsers are built on Blink, WebKit, or Gecko, which is why many of them display pages in very similar ways.

What are browser developer tools?

Developer tools are panels built into browsers that let you inspect and edit the DOM and CSS, debug JavaScript, watch network requests, and measure performance. In most desktop browsers you open them with F12 or by right-clicking a page and choosing Inspect.